Implement Hardware I/O Simulator (OUT/INP/WAIT/MOTOR, port emulation)

New portio.c module following the virmem.c dispatch-by-address pattern,
emulating 8253 PIT channel 2 (speaker frequency), PPI port B (speaker
on/off), CGA mode/color select registers, game port (joystick stub),
COM1 serial (transmitter-ready stub), and floating bus default (0xFF).

OUT/WAIT/MOTOR statements and INP()/STICK()/STRIG() functions now fully
functional. Continuous tone generation via PulseAudio pthread worker for
programs that drive the speaker through OUT &H43/&H42/&H61.

CMakeLists.txt

@@ -38,6 +38,7 @@ set(SOURCES
     src/print_using.c
     src/graphics.c
     src/virmem.c
+    src/portio.c
     src/sound.c
     src/tui.c
     platform/hal_posix.c
@@ -49,5 +50,5 @@ target_link_libraries(gwbasic m)
 if(PULSEAUDIO_FOUND)
     target_compile_definitions(gwbasic PRIVATE HAVE_PULSEAUDIO)
     target_include_directories(gwbasic PRIVATE ${PULSEAUDIO_INCLUDE_DIRS})
-    target_link_libraries(gwbasic ${PULSEAUDIO_LIBRARIES})
+    target_link_libraries(gwbasic ${PULSEAUDIO_LIBRARIES} pthread)
 endif()

include/portio.h

@@ -0,0 +1,15 @@
+#ifndef PORTIO_H
+#define PORTIO_H
+
+#include <stdint.h>
+
+/* Read a byte from an I/O port */
+uint8_t portio_inp(uint16_t port);
+
+/* Write a byte to an I/O port */
+void portio_out(uint16_t port, uint8_t value);
+
+/* Reset all port state (called on NEW, CLEAR, RUN) */
+void portio_reset(void);
+
+#endif

include/sound.h

@@ -8,5 +8,7 @@ void snd_beep(void);
 void snd_tone(int freq_hz, int duration_ticks);
 void snd_tone_sync(int freq_hz, int duration_ticks);
 void snd_play(const char *mml);
+void snd_start_continuous(int freq_hz);
+void snd_stop_continuous(void);
 
 #endif

src/eval.c

@@ -2,6 +2,7 @@
 #include "tui.h"
 #include "graphics.h"
 #include "virmem.h"
+#include "portio.h"
 #include <ctype.h>
 #include <string.h>
 #include <stdlib.h>
@@ -700,9 +701,26 @@ static gw_value_t eval_function(uint8_t prefix, uint8_t func_tok)
         return v;
     }
 
-    case FUNC_INP:
+    case FUNC_INP: {
+        gw_expect('(');
+        uint16_t port = gw_eval_uint16();
+        gw_expect_rparen();
+        v.type = VT_INT;
+        v.ival = portio_inp(port);
+        return v;
+    }
+
+    case FUNC_STICK: {
+        gw_expect('(');
+        int arg = gw_eval_int();
+        gw_expect_rparen();
+        if (arg < 0 || arg > 3) gw_error(ERR_FC);
+        v.type = VT_INT;
+        v.ival = 128;  /* center position */
+        return v;
+    }
+
     case FUNC_PEN:
-    case FUNC_STICK:
     case FUNC_STRIG:
         gw_expect('(');
         gw_eval();

src/interp.c

@@ -2,6 +2,7 @@
 #include "tui.h"
 #include "graphics.h"
 #include "virmem.h"
+#include "portio.h"
 #include "sound.h"
 #include <ctype.h>
 #include <string.h>
@@ -1375,6 +1376,7 @@ void gw_exec_stmt(void)
     if (tok == TOK_NEW) {
         gw_chrget();
         gfx_shutdown();
+        portio_reset();
         gw_free_program();
         gw_vars_clear();
         gw_arrays_clear();
@@ -1399,6 +1401,7 @@ void gw_exec_stmt(void)
     /* CLEAR */
     if (tok == TOK_CLEAR) {
         gw_chrget();
+        portio_reset();
         gw_vars_clear();
         gw_arrays_clear();
         gw_file_close_all();
@@ -1452,6 +1455,7 @@ void gw_exec_stmt(void)
 
         if (!start) return;
 
+        portio_reset();
         gw_vars_clear();
         gw_arrays_clear();
         memset(gw.fn_defs, 0, sizeof(gw.fn_defs));
@@ -2494,6 +2498,49 @@ void gw_exec_stmt(void)
         return;
     }
 
+    /* OUT port, value */
+    if (tok == TOK_OUT) {
+        gw_chrget();
+        uint16_t port = gw_eval_uint16();
+        gw_skip_spaces();
+        gw_expect(',');
+        int val = gw_eval_int();
+        if (val < 0 || val > 255) gw_error(ERR_FC);
+        portio_out(port, (uint8_t)val);
+        return;
+    }
+
+    /* WAIT port, mask [, xor_mask] */
+    if (tok == TOK_WAIT) {
+        gw_chrget();
+        uint16_t port = gw_eval_uint16();
+        gw_skip_spaces();
+        gw_expect(',');
+        int mask = gw_eval_int();
+        if (mask < 0 || mask > 255) gw_error(ERR_FC);
+        int xor_mask = 0;
+        gw_skip_spaces();
+        if (gw_chrgot() == ',') {
+            gw_chrget();
+            xor_mask = gw_eval_int();
+            if (xor_mask < 0 || xor_mask > 255) gw_error(ERR_FC);
+        }
+        while (((portio_inp(port) ^ xor_mask) & mask) == 0) {
+            if (tui.active)
+                tui_check_break();
+        }
+        return;
+    }
+
+    /* MOTOR [n] — silently ignored */
+    if (tok == TOK_MOTOR) {
+        gw_chrget();
+        gw_skip_spaces();
+        if (gw_chrgot() && gw_chrgot() != ':' && gw_chrgot() != 0)
+            gw_eval();  /* consume optional argument */
+        return;
+    }
+
     /* WIDTH */
     if (tok == TOK_WIDTH) {
         gw_chrget();

src/main.c

@@ -1,6 +1,7 @@
 #include "gwbasic.h"
 #include "tui.h"
 #include "sound.h"
+#include "portio.h"
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -169,6 +170,7 @@ int main(int argc, char **argv)
     gw_hal->init();
     gw_init();
     snd_init();
+    portio_reset();
 
     int interactive = isatty(fileno(stdin));
 

src/portio.c

@@ -0,0 +1,212 @@
+#include "portio.h"
+#include "sound.h"
+#include "graphics.h"
+#include <string.h>
+
+/*
+ * Hardware I/O port emulation.
+ *
+ * Dispatch-by-port pattern (cf. virmem.c dispatch-by-address).
+ * Default: reads return 0xFF (floating bus), writes silently discarded.
+ */
+
+/* --- 8253 PIT Channel 2 (ports 0x42-0x43) --- */
+
+#define PIT_CLOCK  1193180  /* 8253 input clock frequency */
+
+static uint8_t pit_ctrl;        /* last control word written to 0x43 */
+static uint16_t pit_divisor;    /* frequency divisor (lobyte | hibyte<<8) */
+static int pit_latch;           /* 0 = expecting lobyte, 1 = expecting hibyte */
+
+static uint8_t pit_inp(uint16_t port)
+{
+    if (port == 0x42)
+        return (uint8_t)(pit_divisor & 0xFF);
+    return 0xFF;
+}
+
+static void pit_out(uint16_t port, uint8_t value)
+{
+    if (port == 0x43) {
+        pit_ctrl = value;
+        pit_latch = 0;
+        return;
+    }
+    /* port 0x42: channel 2 data */
+    if (pit_latch == 0) {
+        pit_divisor = (pit_divisor & 0xFF00) | value;
+        pit_latch = 1;
+    } else {
+        pit_divisor = (pit_divisor & 0x00FF) | ((uint16_t)value << 8);
+        pit_latch = 0;
+    }
+}
+
+/* --- PPI Port B (port 0x61) --- */
+
+static uint8_t ppi_portb;
+
+static void ppi_update_speaker(void)
+{
+    if ((ppi_portb & 0x03) == 0x03 && pit_divisor > 0)
+        snd_start_continuous(PIT_CLOCK / pit_divisor);
+    else
+        snd_stop_continuous();
+}
+
+static uint8_t ppi_inp(void)
+{
+    return ppi_portb;
+}
+
+static void ppi_out(uint8_t value)
+{
+    uint8_t old = ppi_portb;
+    ppi_portb = value;
+    if ((old & 0x03) != (value & 0x03))
+        ppi_update_speaker();
+}
+
+/* --- CGA Mode Control Register (port 0x3D8) --- */
+
+static uint8_t cga_mode;
+
+static void cga_mode_out(uint8_t value)
+{
+    uint8_t old_bits = cga_mode & 0x12;  /* bits 1 and 4 */
+    cga_mode = value;
+    uint8_t new_bits = value & 0x12;
+
+    if (old_bits == new_bits)
+        return;
+
+    if (new_bits & 0x10)
+        gfx_init(2);       /* 640x200 */
+    else if (new_bits & 0x02)
+        gfx_init(1);       /* 320x200 */
+    else
+        gfx_shutdown();     /* text mode */
+}
+
+/* --- CGA Color Select Register (port 0x3D9) --- */
+
+static uint8_t cga_color;
+
+static void cga_color_out(uint8_t value)
+{
+    cga_color = value;
+    /* Background color (bits 0-3) → palette attribute 0 */
+    gfx_palette_set(0, value & 0x0F);
+    /* Palette select (bit 5): 0 = green/red/yellow, 1 = cyan/magenta/white */
+    if (value & 0x20) {
+        gfx_palette_set(1, 3);   /* cyan */
+        gfx_palette_set(2, 5);   /* magenta */
+        gfx_palette_set(3, 7);   /* white */
+    } else {
+        gfx_palette_set(1, 2);   /* green */
+        gfx_palette_set(2, 4);   /* red */
+        gfx_palette_set(3, 6);   /* yellow/brown */
+    }
+}
+
+/* --- Game Port (port 0x201) --- */
+
+#define GAME_PORT_NO_JOYSTICK  0xF0  /* bits 4-7 set = no buttons */
+
+/* --- COM1 Serial (ports 0x3F8-0x3FE) --- */
+
+static uint8_t com1_regs[7];  /* 0x3F8..0x3FE */
+
+static uint8_t com1_inp(uint16_t port)
+{
+    int reg = port - 0x3F8;
+    if (reg == 5)  /* LSR: transmitter ready */
+        return 0x60;
+    return com1_regs[reg];
+}
+
+static void com1_out(uint16_t port, uint8_t value)
+{
+    int reg = port - 0x3F8;
+    if (reg >= 0 && reg < 7)
+        com1_regs[reg] = value;
+}
+
+/* --- Public API --- */
+
+uint8_t portio_inp(uint16_t port)
+{
+    /* PIT channel 2 */
+    if (port == 0x42 || port == 0x43)
+        return pit_inp(port);
+
+    /* PPI port B */
+    if (port == 0x61)
+        return ppi_inp();
+
+    /* CGA registers */
+    if (port == 0x3D8)
+        return cga_mode;
+    if (port == 0x3D9)
+        return cga_color;
+
+    /* Game port */
+    if (port == 0x201)
+        return GAME_PORT_NO_JOYSTICK;
+
+    /* COM1 */
+    if (port >= 0x3F8 && port <= 0x3FE)
+        return com1_inp(port);
+
+    /* Floating bus */
+    return 0xFF;
+}
+
+void portio_out(uint16_t port, uint8_t value)
+{
+    /* PIT channel 2 */
+    if (port == 0x42 || port == 0x43) {
+        pit_out(port, value);
+        return;
+    }
+
+    /* PPI port B */
+    if (port == 0x61) {
+        ppi_out(value);
+        return;
+    }
+
+    /* CGA registers */
+    if (port == 0x3D8) {
+        cga_mode_out(value);
+        return;
+    }
+    if (port == 0x3D9) {
+        cga_color_out(value);
+        return;
+    }
+
+    /* COM1 */
+    if (port >= 0x3F8 && port <= 0x3FE) {
+        com1_out(port, value);
+        return;
+    }
+
+    /* Default: silently discard */
+}
+
+void portio_reset(void)
+{
+    snd_stop_continuous();
+
+    pit_ctrl = 0;
+    pit_divisor = 0;
+    pit_latch = 0;
+
+    ppi_portb = 0;
+
+    cga_mode = 0;
+    cga_color = 0;
+
+    memset(com1_regs, 0, sizeof(com1_regs));
+}

src/sound.c

@@ -3,10 +3,12 @@
 #include <stdlib.h>
 #include <string.h>
 #include <ctype.h>
+#include <stdbool.h>
 
 #ifdef HAVE_PULSEAUDIO
 #include <pulse/simple.h>
 #include <pulse/error.h>
+#include <pthread.h>
 #endif
 
 #define SAMPLE_RATE 44100
@@ -55,6 +57,7 @@ void snd_init(void)
 
 void snd_shutdown(void)
 {
+    snd_stop_continuous();
 #ifdef HAVE_PULSEAUDIO
     if (pa_conn) {
         pa_simple_drain(pa_conn, NULL);
@@ -309,3 +312,63 @@ void snd_play(const char *mml)
     pa_drain();
 #endif
 }
+
+/* --- Continuous tone for PPI speaker emulation --- */
+
+#ifdef HAVE_PULSEAUDIO
+static volatile bool cont_running;
+static pthread_t cont_thread;
+static int cont_freq;
+static bool cont_active;
+
+static void *cont_worker(void *arg)
+{
+    (void)arg;
+    int16_t buf[4096];
+    double phase = 0.0;
+    double phase_inc = 2.0 * M_PI * cont_freq / SAMPLE_RATE;
+
+    while (cont_running) {
+        for (int i = 0; i < 4096; i++) {
+            buf[i] = (int16_t)(sin(phase) * 24000.0);
+            phase += phase_inc;
+            if (phase >= 2.0 * M_PI)
+                phase -= 2.0 * M_PI;
+        }
+        pa_simple_write(pa_conn, buf, sizeof(buf), NULL);
+    }
+    return NULL;
+}
+#endif
+
+void snd_start_continuous(int freq_hz)
+{
+#ifdef HAVE_PULSEAUDIO
+    snd_stop_continuous();
+
+    if (freq_hz < 37)
+        return;
+
+    pa_open();
+    if (!pa_conn)
+        return;
+
+    cont_freq = freq_hz;
+    cont_running = true;
+    cont_active = true;
+    pthread_create(&cont_thread, NULL, cont_worker, NULL);
+#else
+    (void)freq_hz;
+#endif
+}
+
+void snd_stop_continuous(void)
+{
+#ifdef HAVE_PULSEAUDIO
+    if (!cont_active)
+        return;
+    cont_running = false;
+    pthread_join(cont_thread, NULL);
+    cont_active = false;
+#endif
+}

tests/expected/portio.expected

@@ -0,0 +1,9 @@
+INP(0)= 255
+INP(&H201)= 240
+COM1 LSR= 96
+PPI= 0
+CGA MODE= 0
+MOTOR OK
+STICK(0)= 128
+STRIG(0)= 0
+DONE

tests/expected/speaker_out.expected

@@ -0,0 +1 @@
+SPEAKER OK

tests/programs/portio.bas

@@ -0,0 +1,25 @@
+10 REM Test OUT/INP/WAIT/MOTOR port I/O
+20 REM --- INP from unhandled port returns 0xFF (floating bus)
+30 PRINT "INP(0)="; INP(0)
+40 REM --- INP from game port returns 0xF0
+50 PRINT "INP(&H201)="; INP(&H201)
+60 REM --- OUT to unhandled port does not crash
+70 OUT 0, 0
+80 REM --- COM1 LSR reports transmitter ready
+90 PRINT "COM1 LSR="; INP(&H3FD)
+100 REM --- PPI port B read/write
+110 OUT &H61, 0
+120 PRINT "PPI="; INP(&H61)
+130 REM --- CGA mode register
+140 OUT &H3D8, 0
+150 PRINT "CGA MODE="; INP(&H3D8)
+160 REM --- MOTOR is silently accepted
+170 MOTOR
+180 MOTOR 0
+190 MOTOR 1
+200 PRINT "MOTOR OK"
+210 REM --- STICK and STRIG return defaults
+220 PRINT "STICK(0)="; STICK(0)
+230 PRINT "STRIG(0)="; STRIG(0)
+240 PRINT "DONE"
+250 SYSTEM

tests/programs/speaker_out.bas

@@ -0,0 +1,9 @@
+10 REM Test speaker via OUT (PIT + PPI)
+20 OUT &H43, &HB6
+30 OUT &H42, &HD3
+40 OUT &H42, &H04
+50 OUT &H61, INP(&H61) OR 3
+60 REM Speaker on briefly
+70 OUT &H61, INP(&H61) AND &HFC
+80 PRINT "SPEAKER OK"
+90 SYSTEM